1. Field of the Invention
The present invention relates to multicasting, and, in particular, to servers, clients, and methods for multicasting on a computer network.
2. Description of the Related Art
In multicasting, one or more sources transmit a plurality of data signals for potential receipt by one or more receivers in a network. Only one copy of each data signal is transmitted. Each receiver selects which if any of the plurality of signals to receive and process.
Multicasting differs from point-to-point communication, multipoint communication without multicasting, and broadcasting. In point-to-point communication, one copy of data is selectively transmitted from one source to one receiver. In multipoint communication without multicasting, data is copied multiple times, one copy of which is transmitted to each of a set of multiple receivers. In broadcasting, each data signal is transmitted to every receiver in the network without giving the receiver the ability to select only a subset of those transmitted signals to be received.
It is desirable to provide multicasting on a computer network. It is particularly desirable to provide a system for transmitting audio, video, and text data streams for selective receipt by one or more client computers of a computer network. For example, a user would be able to select a television channel comprising audio and video signals for play on the client computer. The user would also preferably be able to control certain aspects of the play of the selected signal. For example, the user would be able to control the volume of the audio component and the size of the display of the video component. Moreover, the user would be able to select a subset of the components of a selected channel for play (e.g., playing only the audio component of a television channel).
It is also desirable that the multicast system support data streams that are received from an external source (e.g., via air transmission or cable) or from a local source (e.g., a VCR). When the client computer provides a windowed environment (such as that provided by Microsoft Windows), the multicast system preferably allows a user to work in one window while the selected video and/or text are displayed in one or more other windows.
The Internet MBONE multicast backbone system is a semi-permanent multicast testbed. MBONE is a virtual network. It is layered on top of portions of the physical Internet to support routing of multicast packets since that function is not integrated into many production routers. The network is composed of islands that can directly support multicast, such as multicast local area networks (LANs) like Ethernet, linked by point-to-point links called "tunnels". The tunnel endpoints are typically workstation-class machines having operating system support for multicast and running the multicast routing daemon.
However, the MBONE system does not provide high-quality multicasting. Audio signals are subject to unacceptable delays that result in non-real-time play at the client computers. In addition, audio and video signals are not related. As a result, the play of audio signals is not synchronized with the play of video signals. The multicasting is therefore of low quality. Moreover, MBONE does not allow the user to select components and control aspects of the selected signal. Furthermore, MBONE does not support the play of a selected signal in a windowed environment.
It is accordingly an object of this invention to overcome the disadvantages and drawbacks of the known art and to provide methods and apparatuses for multicasting multiple signals on a computer network.
It is a further object of the present invention to provide high-quality multicasting of audio, video, and text data streams on a computer network.
It is a further object of the present invention to provide multicasting on a computer network wherein a user may select components of a selected channel for play.
It is a further object of the present invention to provide multicasting on a computer network wherein a user may control certain aspects of the play of a selected channel.
It is a further object of the present invention to provide multicasting on a computer network having client computers that operate in a windowed environment.
Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.